Caption: Scoliosis. Coloured frontal X-ray of the torso of a 42 year old patient with scoliosis. Scoliosis is a lateral (sideways) curvature of the spine that usually starts in infancy or adolescence, and is most often seen in girls. The cause of scoliosis is not known, although occasionally it may be due to a congenital abnormality of the vertebrae (blocks that make up the spine), polio or an injury.